The invention relates to an inductive proximity switch.
A proximity switch is already known from DE 19 740 774 A1. Described there is an inductive proximity switch with two transmitting coils and two receiving coils, the transmitting coil and the receiving coils being respectively disposed parallel to one another. The mode of operation of the proximity switch described there is based on the two receiving coils being influenced alternating electromagnetic fields which pass through and are generated by a trip.
A further proximity switch is already known from DE 40 31 252 C1. This document describes a proximity switch in which each transmitting coil is acted upon by an oscillator with an alternating current. Right next to the transmitting coil there are two receiving coils, spaced slightly apart from one another, which are connected in series but wound in opposite directions. The position of the receiving coils is chosen such that, when the trip does not approach, an aggregate current close to zero is induced in the two differential coils.
If a metal trip approaches the transmitting coil, eddy currents are generated in the trip. These eddy currents generate an opposing field with respect to the exciting field. This opposing field has a different intensity in the two receiving coils. It consequently induces voltages of different magnitudes in the two receiving coils. The differential signal of these two voltages deviates from zero and can be amplified to form the output signal.
DE 100 39 610 relates to a proximity switch with an oscillating circuit in which two windings are provided, which by analogy with the proximity switches described above are likewise electromagnetically coupled to one another.
DE 198 50 749 is concerned with an inductive proximity switch operating two detector coils and a transmitting coil, in which the coils are formed as planar coils and likewise lie in the field generated by the induced eddy current field.
DE 100 57 773 discloses a proximity switch in which a multiplicity of coils are associated with a printed circuit board as planar coils lying next to one another.
On the basis of the prior art cited at the beginning, the object of the invention is to take measures which increase the switching distance.